1. Field of the Invention
The present invention relates to the field of displaying technology, and in particular to a polysilicon manufacturing method that controls the growth direction of polysilicon.
2. The Related Arts
The displaying technology has been under fast development recently. A flat panel display device is significantly different from a traditional video image displaying device by adopting totally different displaying and manufacturing technology. The traditional video image displaying device is generally based on a cathode ray tube (CRT), from which a flat panel display device differs primarily concerning changes made in respect of weight and size (thickness). Generally, a flat panel display device has a thickness not greater than 10 centimeters, among the other differences associated with various technical aspects, such as theory of displaying, manufacturing material, manufacturing process, driving for displaying video images.
The flat panel display device possesses features such as being completely flattened, being light and thin, and energy saving and currently undergoes progresses toward high PPI (pixels per inch), low power consumption, and high integration. Amorphous silicon, which is conventionally used, due to inherent limitation, cannot suit the above described needs and polysilicon is considered the best candidate for substituting amorphous silicon for polysilicon is fit for the needs for future developments of the flat panel display device. Thus, low-temperature polysilicon (LTPS) displaying technology has become a new favorite of the displaying field.
As links of the technical cores of the low temperature polysilicon displaying technology, the manufacturing process and material behavior of polysilicon determine the performance of a display device. The manufacturing processes of polysilicon that are currently known include: low pressure chemical vapor deposition (LPCVD), solid phase crystallization, metal induction, and laser annealing. The most commonly used process in the industry is the laser annealing operation, which uses the high temperature generated by a laser beam to melt amorphous silicon for re-crystallization to form polysilicon. As shown in FIG. 1, a schematic view is given to illustrate the process flow of a conventional way of manufacturing polysilicon, wherein, specifically, a silicon nitride (SiNx) layer 200 is first formed, through deposition, on a glass substrate 100; a silicon oxide (SiOx) layer 300 is then formed, through deposition, on the silicon nitride layer 200; an amorphous silicon (a-Si) layer 400 is then formed, through deposition, on the silicon oxide layer 300; the amorphous silicon layer 400 is subjected to rinsing with hydrogen fluoride (HF); and then the rinsed amorphous silicon layer 400 is irradiated by a laser 500 to carry out a laser annealing operation by which crystallization of the amorphous silicon contained in the amorphous silicon layer 400 is caused to form a polysilicon layer 600. Although such a manufacturing process can better the result of crystallization through adjustment of the parameters of the laser, it is generally not possible to effectively control the growth direction of the polysilicon 600 during the annealing operation so that it is not possible to effectively control where a grain boundary appears.